Reel-to-reel tape transport systems are widely employed in connection with magnetic tape recorders. For certain applications, it is necessary automatically to terminate playing of the tape from one reel to another in response to either of the reels being substantially completely filled with tape, i.e., in response to the other reel being substantially completely empty of tape. In the past, it has generally been the practice to provide electrical actuation of a mechanism to stop the tape transport mechanism in response to one of the reels being fully wound with, or completely empty of, tape. In certain situations, either for backup of the electrical system or as a primary brake means for preventing overwind of tape from a reel being emptied, electrical systems are not desirable because of reliability factors. In particular, if there is a malfunction to an electrical sensing component or any of the circuitry or power supplies for the electrical component, there is a failure to the system for deactivating the tape transport mechanism and tape will be completely exhausted from one of the reels, with obvious deleterious effects.